Nitric oxide abatement with polymeric cobalt(III) chelates

Abstract

An NO abatement process wherein an NO-containing fluid is contacted with a polymeric cobalt(II) dioxygen diamine complex. The aqueous solution is recovered, purified by membrane separation to remove low molecular weight reaction products, optionally electrolytically regenerated, and recycled for the NO-containing gas contact. The cobalt(II) is complexed with an amine-containing polymer such as polyethyleneimine free of acidic, e.g. carboxylate, chelating groups.

What is claimed is: 
     
       1. A method for abating nitric oxide in a fluid stream, comprising the steps of: (A) contacting a fluid stream containing nitric oxide with an aqueous solution of a polymeric cobalt(II) diamine dioxygen complex, wherein said complex is obtained by (a) complexing (i) a cobalt(II) salt with (ii) a water soluble, basic polymer comprising polyethyleneimine containing secondary amine groups, wherein the molar ratio of said amine groups to cobalt(II) is from 3 to 6, and (b) oxygenating the resulting polymeric cobalt(II) diamine complex;   (B) recovering aqueous solution resulting from said contact with said fluid stream in step (A);   (C) purifying said recovered aqueous solution to remove low molecular weight reaction products; and   (D) recycling the purified solution from step (C) for reuse in the aqueous solution of step (A).   
     
     
       2. The method of claim 1, wherein said fluid stream contains oxygen. 
     
     
       3. The method of claim 1, wherein said fluid stream is essentially free of sulfur oxides. 
     
     
       4. The method of claim 1, wherein said water soluble polymer has a molecular weight between about 500 and 1,000,000. 
     
     
       5. The method of claim 1, wherein said polymer is essentially free of acidic chelating groups in excess of a 1:1 molar ratio of said acidic groups to said amine groups. 
     
     
       6. The method of claim 1, wherein said purification is by ultrafiltration or dialysis. 
     
     
       7. The method of claim 1, wherein said purification removes at least a portion of said reaction products with a molecular weight less than 1000. 
     
     
       8. The method of claim 1, further comprising the step of electrolytically regenerating said recovered aqueous solution. 
     
     
       9. A method for abating nitric oxide in a fluid stream, comprising the steps of: (A) contacting a fluid stream containing oxygen and nitric oxide in a contacting zone with an aqueous solution of a polymeric cobalt(II) diamine complex effective to produce a fluid stream of reduced nitrogen oxide content, wherein said complex is obtained by complexing (i) a cobalt(II) salt with (ii) polyethyleneimine having a molecular weight between about 500 and 1,000,000 and containing secondary amine groups, wherein the molar ratio of said amine groups to cobalt(II) is from 3 to 6, and wherein said polyethyleneimine is free of acidic chelating groups in an amount equal to or in excess of a 1:1 molar ratio of said acidic groups to said amine groups;   (B) recovering the resulting aqueous phase produced in step (A);   (C) concentrating the aqueous phase recovered in step (B) by membrane separation by effectively removing a portion of reaction products having a molecular weight below 1000; and   (D) recycling the concentrated aqueous phase from step (C) to the contacting zone in step (A).   
     
     
       10. The method of claim 9, wherein said fluid stream is essentially free of sulfur oxides. 
     
     
       11. The method of claim 9, wherein said fluid stream comprises gas turbine flue gas. 
     
     
       12. The method of claim 9, wherein said polyethyleneimine has a molecular weight of between about 1,000 and 500,000. 
     
     
       13. The method of claim 9, wherein said membrane separation comprises ultrafiltration effective to remove reaction products with a molecular weight below 500. 
     
     
       14. The method of claim 9, wherein said molar ratio of secondary amine groups to cobalt(II) is between about 4 and 5. 
     
     
       15. The method of claim 9, further comprising the step of electrolytically regenerating cobalt(III) in the aqueous phase recovered in step (B) to cobalt(II). 
     
     
       16. The method of claim 9, wherein said contacting zone is maintained at a temperature between about 25° C. and 60° C. 
     
     
       17. The method of claim 9, wherein said polyethyleneimine is unsubstituted. 
     
     
       18. The method of claim 9, wherein said polyethyleneimine is essentially free of acidic substituents. 
     
     
       19. The method of claim 9, wherein the fluid stream is flue gas cooled to below about 60° C.